While a variety of methods have been known as atmospheric pressure ionization methods, attention has been paid to DART (Direct Analysis in Real Time) recently (see Patent Document 1).
DART is a method for colliding an atom or molecule in an electronically excited state with water in atmosphere to cause penning ionization thereof and adding a produced proton to a sample to cause ionization thereof.
For example, when a helium in a metastable excited state He (23S) is used, it is possible to ionize a sample M as follows.He(23S)+H2O→H2O+*+He(11S)+e−H2O+*+H2O→H3O++OH*H3O++nH2O→[(H2O)nH]+[(H2O)nH]++M→MH++nH2O
However, there is a problem in that it is difficult to analyze a polymer compound.